Archaeopteryx is the fossil that proved Darwin right. It is the oldest known fossil bird and helps demonstrate that all birds, including modern ones, are dinosaurs. Although the first fossil of this Jurassic species was found 160 years ago, a newly analyzed specimen now presents new and interesting data.

Thanks to an exhaustive analysis of the so-called Chicago Archaeopteryx, an exceptionally well-preserved specimen that has recently been incorporated into the Field Museum’s collection, scientists have managed to document anatomical details, soft tissues, and feathers that had never before been observed in another specimen of this species.

The fossil is approximately the size of a pigeon and was found in the Solnhofen limestone deposits in Germany, the same area where all other known specimens of Archaeopteryx have been discovered. Previously held in a private collection, it was acquired by the Chicago museum in August 2022.

Archaeopteryx birds dinosaurs
Illustration showing Archaeopteryx in life, including its tertial feathers that would have helped it fly. Credit: Michael Rothman

According to Jingmai O’Connor, associate curator of fossil reptiles at the Field Museum and lead author of the study published in the journal Nature, the first impression upon receiving the fossil was one of excitement, though also uncertainty: After so many years of research on Archaeopteryx, we didn’t know if this specimen could offer anything new. However, the quality of its preservation, combined with an extremely meticulous preparation, has allowed us to access an unprecedented wealth of information, from the tip of the snout to the end of the tail, she states.

The fossil’s preparation was led by Akiko Shinya, the museum’s chief fossil preparator, who worked on it for over a year. Given the fragility of the bones, which are hollow and tiny, and the hardness of the surrounding rock, each fragment of stone had to be removed with microscopic precision, carefully determining where the fossil ended and the rock began, as both have almost identical hues.

The team used advanced technological tools such as computed tomography (CT scans), which made it possible to visualize the interior of the rock and plan the precise extraction of the bones. For the first time, a complete specimen of Archaeopteryx was scanned in 3D using this technology, and the resulting data has been made available to the scientific community.

The use of ultraviolet light revealed structures in the fossil invisible to the naked eye, such as scales on the underside of the toes—something possible due to the peculiar fluorescence exhibited by all Solnhofen fossils. The researchers successfully preserved the bony structures and soft tissues and also identified features that were likely present in other specimens but were destroyed due to the use of more aggressive preparation techniques.

Archaeopteryx birds dinosaurs
The Chicago Archaeopteryx. Credit: Delaney Drummond / Field Museum

In their analysis, the researchers focused mainly on the head, limbs, and wing feathers. The bones of the palate revealed clues about the evolution of cranial kinesis, a trait present in modern birds that allows the beak to move independently of the skull—something that may have contributed to their diversification into more than 11,000 species.

The preserved soft tissues in the hands and feet have supported the hypothesis that Archaeopteryx frequently walked on the ground and may have even climbed trees. But perhaps the most important finding is the wing feathers, specifically a set of long feathers on the upper arm known as tertials, which had never before been observed in this species.

Compared to modern birds, Archaeopteryx had a very long humerus, which created a gap between the primary and secondary wing feathers and the body, O’Connor explains. That gap reduces lift during flight. But modern birds solve this problem with tertial feathers that fill that space. The Chicago specimen is the first in which these feathers can be seen, indicating that Archaeopteryx had a wing configuration that allowed it to fly effectively, unlike other dinosaurs that only had feathers up to the elbow.

This discovery, according to O’Connor, reinforces the idea that flight may have evolved more than once among dinosaurs. And although the study focuses on various anatomical aspects, the researcher emphasizes that only the surface of the knowledge this fossil can provide has been scratched: We are learning new and exciting things from almost every preserved part of the body. This paper is just the tip of the iceberg.

SOURCES

Field Museum

O’Connor, J., Clark, A., Kuo, PC. et al. Chicago Archaeopteryx informs on the early evolution of the avian bauplan. Nature (2025). doi.org/10.1038/s41586-025-08912-4

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